[UPBEAT MUSIC] ROSEMARY MOSCO: I thought, oh, my goodness. I have to do a comic about an animal with a zillion different butts?

D PETERSCHMIDT: Hi. Welcome back to Universe of Art, a podcast from Science Friday about artists who use science to bring their work to the next level. I'm D Peterschmidt. So when I think about some of my favorite stories I've worked on, today's episode is one that usually shoots to the top of my mind. It's got everything-- sea cucumber anuses, the evolutionary history of the digestive system, exactly 50 uses of the word "butt," but I can explain.

Last year, the SciFri staff-- we saw this tweet about butts that caught our attention. It was from researcher Dr. Maureen Berg asking a very important question. "Does anyone know of an animal that has a few butts? Like, more than one, but fewer than a hundred?" And it spurred all these other questions. How does science define a butt? Why are invertebrate butts so much more interesting than vertebrate behinds? And what's the deal with this group of illustrators and scientists who are dedicating a whole week to educating the public about these special posteriors?

And it kind of sent me down a delightful rabbit hole. Turns out I'm now on Team InverteButt. Sorry, but vertebrate butts are just kind of boring to me now. Also, something we couldn't put in the original segment were some responses that our audience had when we asked them, how would you define an animal butt? Which was one of the core questions of this segment. And I just have to quickly play you a voice memo response we got from audience member KB.

SPEAKER 3: I'd like to take this opportunity to honor A Tribe Called Quest in my response.

[HIP HOP MUSIC]

(RAPPING) What is a butt if it doesn't excrete? What is a cheek if it doesn't make a seat?

D PETERSCHMIDT: I really can't think of a better introduction to this story. So welcome to the wild world of invertebrate butts. You mind reading the tweet that you sent out back to me?

MAUREEN BERG: Hold on a second. Let me get it up. "Hello. Does anyone know of any animal that has a few butts? Like, more than one, but fewer than a hundred? And I'm generally talking butts as the anus, but I'm open to other interpretations."

D PETERSCHMIDT: That's Dr. Maureen Berg, a scientist at the Joint Genome Institute at Berkeley National Lab. You probably aren't sitting around thinking about animal butts, but Maureen is a part of a group of scientists and illustrators who think about them a lot. She got her start in invertebrate biology, and invertebrate butts-- or InverteButts-- have become one of her passions. She's even given public talks about them.

MAUREEN BERG: Now I'm known as, like, the invertebrate butt girl on Twitter. So any time any kind of new animal butt thing comes up, I always get tagged in these. It's just, like, a standard procedure at this point. Even though I do no research in this field, just once again, I'm just the loudest person about this.

D PETERSCHMIDT: Yeah. How do you feel about that, of that being your calling card now on Twitter?

MAUREEN BERG: I'm honored, honestly. It's an honor.

D PETERSCHMIDT: So now, people tag her in tweets when certain discoveries are made.

MAUREEN BERG: There's a recent worm that was discovered that has hundreds of butts.

D PETERSCHMIDT: That worm, Ramisyllis multicaudata, isn't like most worms. Its body segments and branches out in multiple places, looking more like a connected series of cracks in a dried-up riverbed than a traditional worm, and at the end of each of these dozens of branches is an anus.

ROSEMARY MOSCO: I'm always looking for comic fodder, and that one kind of wrote itself.

D PETERSCHMIDT: Turns out, Maureen isn't the only one fascinated with invertebrate butts on Twitter.

ROSEMARY MOSCO: I thought, oh, my goodness. I have to do a comic about an animal with a zillion different butts.

D PETERSCHMIDT: Science Illustrator Rosemary Mosco put together a chat group appropriately named Butt Chat, and invited other butt-enthusiastic illustrators and scientists. I mean, what were your initial reactions to just being involved in this project?

AINSLEY SEAGO: A complete lack of surprise.

D PETERSCHMIDT: Dr. Ainsley Seago, the Curator of Invertebrate Zoology at the Carnegie Museum of Natural History in Pittsburgh, was one of the researchers who got invited to this Butt Chat. And like Maureen, she'd also given a talk about bug butts before. She started a small document with some of her favorite butt facts, threw it into the chat, and the other members started adding to it.

AINSLEY SEAGO: I think at one point, I said, oh, no, we've opened Pandora's butt.

[LAUGHTER]

Because there were so many different pieces of information flying in this chat.

D PETERSCHMIDT: The group decided they'd team up and use their combined science and illustration powers for good by making comics about the back ends of the backbone list. They're calling their celebration InverteButt Week, like Shark Week or Cephalopod Week, but for invertebrate butts.

AINSLEY SEAGO: It's just a chance for some people who do science communication to do the silliest thing that they can possibly think of. We love talking about this stuff. Sometimes, you get really tired of only covering the depressing news or only covering the extremely technical details, and this is something that's both educational and delightful, frankly.

D PETERSCHMIDT: So we've got lots of information, but not an answer to the big question. What even is a butt?

MAUREEN BERG: There's been discussions on Science Twitter in the past about, what is a butt? Is it just, like, you know, the back end of an animal, or is it, like, the anus?

D PETERSCHMIDT: Some purist researchers are a little anal about this and believe that the word "butt" should only be used when referring to fleshy buttocks. Maureen and Ainsley have more generous views on this.

AINSLEY SEAGO: You got one end where food comes in and one end where poop goes out. That second end is, in my personal definition, the butt. It does get challenging when you think about questions like, if a bug wore pants, would it wear them like this or like this? But I think we can conclude that what we, in insect morphology terms, refer to the abdominal apex, is, I would say, with zero ambiguity, the butt region.

MAUREEN BERG: So yeah. Context is very important on how you define it, but I'm flexible on definition.

D PETERSCHMIDT: And for a bit more context, we have to go back hundreds of millions of years ago to the Earth's oceans. Most animals back then didn't have what we think of as a butt. Most just had a single multipurpose hole for eating and excreting. The descendants of some of these animals are still with us, like coral and jellyfish, but as you might imagine, that one-road setup had some serious drawbacks.

MAUREEN BERG: And so the idea with that is, like, you can only eat, and then you digest your food, and then you can get rid of your waste, whereas with us, as humans, you can continue to eat as you're digesting, you know? You don't need to wait for your whole digestive system to clear out before you can eat again. So the whole even concept of evolving an anus allows you to basically eat and digest at the same time. So it's a little bit more efficient.

D PETERSCHMIDT: The evolutionary marvel of the digestive system-- and, subsequently, the anus-- was a big deal for life on Earth. Animals got more out of their meals, bodies lengthened and grew bigger and developed better ways to move around, like swimming, walking, and flying, rather than, say, just existing, floating in the water like a jellyfish. What's about that you think that more people should know about?

MAUREEN BERG: I mean, my favorite animal butt to talk about is the sea cucumber butt, just because it does a lot of weird things. Like, it's not just one weird thing. It does a lot. A lot of sea cucumber's butts act as homes for other animals. Like, you have the fish. You have crabs. You have a lot of things that live in the butt.

And because, maybe, you don't want just any animal living in your butt, a lot of sea cucumbers have anal teeth to prevent certain animals from inhabiting their butt, essentially. Because what some will do is they'll get into the butt, and they'll start kind of munching and gnawing on the gonads and stuff, which is obviously bad. So they kind of have it all. They have eating, breathing, defense, apartment building-- like, they have it all. And I really admire it.

D PETERSCHMIDT: It would get, like, the most versatile butt award.

MAUREEN BERG: Exactly.

FRANZ ANTHONY: I want to talk about the face mite. The best part about them is that they don't have butts.

D PETERSCHMIDT: Franz Anthony is another science illustrator working with Rosemary on the project.

FRANZ ANTHONY: The problem, when someone doesn't have butts, is that they can't poop. So throughout their life, their body just gets longer and longer as their poop accumulates inside. And then once they die, they just burst open, and then the mite poop is basically all over people's faces. And I think that's really, really fun.

D PETERSCHMIDT: And I don't like to pick favorites, but Ainsley's preferred butt might be mine now, too.

AINSLEY SEAGO: One of my absolute favorites is the Neuropteran family virodhi.

D PETERSCHMIDT: They're a type of lacewing, small insects with large, clear wings, and their larvae live in termite mountains, which is a pretty dangerous place to grow up. Termites are essentially soldiers. They're territorial and dangerous, and they don't want any intruders in their home. So how do these seemingly defenseless larvae defend themselves?

AINSLEY SEAGO: When termites approach them, they turn around and wave their butt in its face, and release an invisible but powerful gas that knocks out the termites almost instantly. So they're essentially farting them to death as a form of defense. And it's just one of the most beautiful things of that nature has come up with in her infinite wisdom.

That's the central thesis of InverteButts Week, which is, let there be joy. It's OK to have yourself a secret little chortle at an insect that's farting another animal to death. That's pretty great.

D PETERSCHMIDT: I wanted to end on this question, which is, why should we care about butts? I'll take my answer off the air.

[LAUGHTER]

ROSEMARY MOSCO: Listen, I don't think that butts are necessarily the most important thing going on right now in society. But I think that butts are something delightful to think about. And looking at one particular body part of an animal can be a way to look at an entirety of an animal, and look at the way that it experiences the world.

FRANZ ANTHONY: Yeah. I think butt in general is just really funny, because it's really accessible. Even kids understand it. So it is a gateway for kids to understand bigger concepts.

ROSEMARY MOSCO: And adults, too. I mean, I think, like, adults are already so excited about anything goofy and butt-related. So I think we all need to hop aboard the butt train and ride it to science town.

[LAUGHTER]

I'm so sorry.

D PETERSCHMIDT: No.

[LAUGHTER]

The team behind InverteButt Week is planning to do this again next March. But in the meantime, though, you can check out illustrations from Rosemary and Franz and others on her site. That's at sciencefriday.com/butts. For Universe of Art, I'm D Peterschmidt, national butt correspondent.

[UPBEAT MUSIC]

Universe of Art is hosted and produced by me, D Peterschmidt, and I also wrote the theme music. Charles Bergquist and John Dankosky provided production assistance, and our show art is illustrated by Abelle Hayford, and support for Science Friday's science and arts coverage comes from the Alfred P. Sloan Foundation. We'll be back in two weeks. See ya.

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